const start = Date.now();
setTimeout(function f1() {
  console.log('setTimeout', Date.now() - start);
}, 200);

const fs = require('fs');

fs.readFile('./index.js', 'utf-8', function f2() {
  console.log('readFile');
  const start = Date.now();
  while (Date.now() - start < 300) {}
});
